Related Party Transactions - Franchisees (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 24, 2017	Jun. 25, 2017	Mar. 26, 2017	Dec. 25, 2016	Sep. 25, 2016	Jun. 26, 2016	Mar. 27, 2016	Dec. 31, 2017	Dec. 25, 2016	Dec. 27, 2015
Related party transactions
Total revenues	$ 467,606	$ 431,709	$ 434,778	$ 449,266	$ 439,619	$ 422,442	$ 422,964	$ 428,595	$ 1,783,359	$ 1,713,620	$ 1,637,375
Accounts receivable - affiliates	86				105				86	105
Franchisees owned by related parties
Related party transactions
Commissary and other sales									2,619	2,620	2,730
Franchise royalties and fees									776	413	394
Total revenues									3,395	3,033	$ 3,124
Accounts receivable - affiliates	$ 86				105				$ 86	105
Accounts payable - affiliates					$ 12					$ 12